Antenna circuit



June 13, 1950 1 H. FINNEBURGH, JR., Er AL 2,511,574

ANTENNA CIRCUIT Filed sept. 3. 1949 U INV EN TOR.

. BY icas/ 27' S. WE/

Patented June 13, 1950 UNITED STATES PATENT OFFICE Robert S. Weiss,Cleveland, Ohio, assignors 'to The Gabriel Company, Cleveland, Ohio, acorporation vof Ohio Application September 3, 1949, Serial No. 113,998

(Cl. Z50-'433) 4 Claims. I

This invention relates to an antenna circuit or system and moreparticularly to an automatic antenna selector system.

The principal object of the invention is the provision in amulti-antenna system including a high frequency antenna and a lowfrequency antenna of means for automatically maintaining in the circuitthe desired antenna and -for isolating from the circuit the undesiredantenna, depending upon whether the high or low band receiving apparatusas, for example, a television set, is adjusted for high frequency or lowfrequency reception.

Another object is to ,provide an improved and novel electrical antennaselector system which may be advantageously employed wherever a high andlow band antenna is connected to a common transmission or lead-in line.

A further object is to provide an electrical antenna selector systemwhich may be advantageously employed in multi-antenna arrays whichinclude high and low band antennas.

Another object is to provide an antenna system for use with radio andtelevision receiver sets capable of receiving both high and lowfrequency signals and which system includes a high frequency antenna anda low frequency antenna together with simple and efficient meansdirectly associated with the antennas for automatically isolating thelow frequency antenna from the circuit when the set is adjusted for highfrequency reception or for automatically isolating the high frequencyantenna from the circuit when the set is adjusted for low frequencyreception.

Further and additional objects and advantages not expressly set forthabove will become apparent during the detailed description of anembodiment of the invention which is to follow.

The accompanying drawing is a diagrammatic or schematic showing of anantenna system embodying the invention and including high frequency andlow frequency antennas connected to a common transmission or lead-inline.

For the purpose of explaining the invention a high frequency antenna Iand a low frequency antenna il are illustrated. The antennas Hl and llare shown for illustrative purposes as of the folded dipole type but itwill be understood they could be of the straight dipole type as well.

A wiring harness connects the terminals of the antennas lil and Il andcomprises wires I6 and Il connected, respectively, to the arms I2 and I4and to the arms I3 and I5 of the antennas IIJ and Il.

YIt will be understood that the wires I6 and l1 of the wiring harnessare connected to the arms of the antennas by the terminals at the endsthereof which are electrically spaced apart to provide an electricalgap. A transmission or lead-in line extending to the receiving apparatus(not shown) is connected to the wiring harness and comprises wires Itand I9 connected, respectively, to the Wires l5 and Il of the harness.

The Wires forming the wiring harness and the transmission or lead-inline are of similar size and form and the wires of the transmission orlead-in line are connected to the harness at a predetermined andcritical point as, for in stance, at a location one-quarter wave lengthat high frequency from the lcW frequency antenna as indicated by thearrowed lines A and onequarter wave length at low frequency from thehigh Vfrequency antenna as indicated by the arrowed lines B.

In carrying out .the invention a low frequency series resonant circuitis in the gap between the arms l2 and i3 of the high frequency antennaHl and is connected to the terminals of this antenna, and a highfrequency series resonant circuit similarly is in the gap between thearms I4 and l5 of the low frequency antenna Il.

The low frequency series resonant circuit may comprise a suitable radiofrequency choke coil 2S and a condenser 2l in series therewith, whilethe high frequency series resonant circuit similarly may comprise aradio frequency choke 'coil 22 and a condenser '23 in series therewith.

As illustrative of a specific arrangement which may .be employed withrespect to the wiring harness and the low and high frequency seriesresonant circuits the following is set forth:

The wiring harness may be constructed of 300 ohm twin lead Wire whilethe transmission line may be connected to the harness at 111/2. from thellow frequency antenna H and at 34% from the high frequency antenna it,assuming such distances to' correspond, respectively, to onequarter wavelength at high frequency and cnequ'arter wave length kat low frequency.

The low frequency series resonant circuit may consist of a .5 microhenrychoke coil 2!) in series with a 14 micromicrofarad cirainic'cncondenser. The high frequency series yresonant circuit may consist of a.22 microhenry choke coil 22 in series with a 3 micromicrofaradceramicon condenser 23. The series resonant circuits comprising thesmall radio frequency choke coils and the small ceramicon condensers can'be formed as units and placed directly across the gaps between the armsof the antennas and on the antenna insulators, thus providing a simplearrangement and a neat appearance.

The antenna system hereinbefore described functions as follows: Assumingit is desired for the receiving set to receive high frequency signals,the high frequency series resonant circuit consisting of the coil 22 andthe condenser 23 and extending across the low frequency antenna IIapproaches zero impedance. This W or zero impedance at the point wherethe transmission line is connected to the wiring harness that isone-quarter high frequency Wave length along the harness from the lowfrequency antenna II is reflected back as a very high impedance,wherefore the low frequency antenna II is electrically disconnected orisolated from rthe antenna system. The low frequency series resonantcircuit consisting of the coil 20 and condenser 2I and placed across thehigh frequency antenna Il has substantially no effect at high frequencyon the antenna I since the low frequency series resonant circuit attainsa high impedance at high frequencies and in electrical effect isdisconnected from the antenna I0, wherefore the antenna I functions inthe ordinary manner of a high frequency antenna for the reception ofhigh frequency signals.

Assuming that the receiving set has been adjusted for the reception ofsignals at low frequency then the high frequency antenna I0 isautomatically electrically isolated from the system and the lowfrequency antenna I I functions as an ordinary low frequency antenna. Inthis situation the low frequency series resonant circuit composed of thecoil 20 and the condenser 2I across the gap of the high frequencyantenna I0 attains substantially to zero impedance and this lowimpedance is reflected back as an extremely high impedance at the pointwhere the trans' mission line is connected to the wiring harness, thatis at a point which is one-quarter wave length at low frequency from theantenna I0. Consequently the high frequency antenna I0 is. isolatedelectrically from the system.

Under this latter condition the high frequency series resonant circuitcomposed of the coil 22 and condenser 23 and placed across the low bandantenna goes to a very high impedance on the low frequency signals andthus is effectively electrically disconnected from the low frequencyantenna I I and has no effect thereon.

From the foregoing description it has been delineated that the inventionprovides a simple and efficient antenna system for use with receivingapparatus of the high and low frequency type and which system includeshigh and low frequency antennas and means for automatically andelectrically isolating from the circuit one or the other of theantennas, depending upon whether the receiving apparatus is adjusted forhigh frequency reception or for low frequency reception.

It will also have been noted that the advantages accomplished by theantenna system em' bodying the invention eliminates the necessity ofemploying expensive selective and operative equipment for isolating oneor the other of the antennas and necessitates only the use of simple,inexpensive low and high frequency series resonant circuits and theproper connection of the transmission line to the wiring harness betweenthe antennas. Once the system is installed the electrical isolation ofeither the low or the high frequency antenna is automatically obtainedmerely by adjusting the receiving apparatus for high or low frequencyreception as the case may be.

Although a. preferred embodiment of the lnvention has been illustratedand described herein, it will be understood that the invention issusceptible of various modifications and adaptations within the scope ofthe appended claims.

Having thus described our invention, we claim:

1. An antenna system for high and low wave frequency receptioncomprising a high frequency dipole antenna, a low frequency dipoleantenna, a wiring harness interconnecting the terminals of saidantennas, a'low frequency series resonant circuit between the terminalsof said high frequency antenna, a high frequency series resonant circuitbetween the'terminals of said low frequency antenna, and a transmissionline adapted to extend to suitable high and low band receiving apparatusand connected to said wiring harness at a point so located with respectto said antennas that for high frequency reception the substantiallyzero impedance in the high frequency series resonant circuit across thelow frequency antenna will be reflected back at said point of connectionas a very high impedance, thus electrically and automatically isolatingthe low frequency antenna and similarly for low frequency reception thesubstantially zero impedance in the low frequency series resonantcircuit across the high frequency antenna will be reflected back at saidpoint of connection as a very high impedance thus electrically andautomatically isolating the high frequency antenna.

2. An antenna system as dened in claim l and wherein the low and highfrequency series resonant circuits each includes a radio frequency chokecoil in series with a condenser.

3. An antenna system as defined in claim l and wherein the transmissionline is connected to said wiring harness at a point-one-quarter wavelength at low frequency from said high frequency antenna and one-quarterwave length at high frequency from said low frequency antenna.

4. An antenna system for high .and low wave frequency receptioncomprising a high frequency vdipole antenna, a low frequency dipoleantenna, a wiring harness interconnecting the terminals of saidantennas, a low frequency series resonant circuit between the terminalsof said high frequency antenna, a high frequency series resonantcirlcuit between the terminals of said low frequency antenna, saidresonant circuits each including a radio frequency choke coil in serieswith a condenser, and a transmission line connected to said wiringharness at a point one-quarter wave length at low frequency from saidhigh frequency antenna and one-quarter wave length at high frequencyfrom said low frequency antenna.

LEWIS H. FINNEBURGH, Jp.. ROBERT S. WEISS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2, 474,480 Kearse June 28, 1949OTHER REFERENCES Electronics, May 1947, page 99.

Oak Ridge Antennas Your Best Move, 239 East 127th Street, New York 35,New York, Technical Data, page 9.

